The long term objectives of this proposal are (l) to determine if testis-specific cytochrome ct I is an auto- or isoantigen, (2) to determine if auto- or isoimmunity to testicular cytochrome ct I is a casue of infertility, and (3) to determine if active immunization with testicular antigens or passive immunization with antibodies to testicular antigens could be used for immunological control of fertility in the future. The immediate goals are (l) the isolation and characterization of testis-specific cytochrome ct I from rabbit testes, (2) the isolation of cytochrome ct I-specific peptide by the CNBr cleavage method, (3) the production of specific antiserum to testis-specific cytochrome ct I and cytochrome ct I-specific peptide, (4) the development of radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) for cytochrome ct I and anti-cytochrome ct I antibodies, and (5) preliminary anti-fertility experiments on female rabbits by active isoimmunization with a cytochrome ct I-specific peptide.